Why do different species and strains of mushrooms have different highs?

All active Psilocybe mushrooms contain the same main substances which are psilocybin, psilocin and to a lesser degree baeocystin and norbaeocystin.

All active Psilocybe mushrooms contain the same main substances which are psilocybin,
psilocin and to a lesser degree baeocystin and norbaeocystin. The amounts and
proportions of those 4 key components varies among different species and strains.
Alongside with those 4 main components there are many other
substances, which by them self don't have a described psychoactive effect,
but might very well have a slight modifying effect on the psychoactive properties
of the key components.

Another likely cause for the different effect of different mushrooms is the
influence of the effect of stomach contents and set and setting on the psychedelic experience.
The use of any hallucinogen involves "set," i.e. mind-set, mood, emotional
state and "setting," the environment and/or people with whom one is
tripping at the time. The combination of set and setting in conjunction with
the effects of the drug produce the kind of trip one has, good or bad. People
do experience psychotic breaks from reality in a bad trip and this can be extremely
traumatic with long-term and lingering after effects. A good trip can be very
euphoric and transcendent in comparison. Which you’ll get is again, dependent
on set, setting, the drug and certain amount of luck and randomness.